I've just gotten my first bike rack and panniers, since I'm commuting to/from school more. I ride a Fuji Crosstown hybrid, and I have a rear rack that mounts to the seat post and the frame. Friday was my first ride with a messenger-style pannier bag attached to the rack, and things went wonderfully. Today I had that same bag attached to one side and a grocery bag holder on the other side (not to carry groceries, but for my lunch bag, clothes, etc.).

All was fine on the trip to campus and for most of the way home from school. However, the wind picked up on my way home and toward the end of my ride, the front end of my bike felt a little wobbly, especially at lower speeds. I pulled over to make sure that my front wheel and handle bars were okay, and I didn't feel any play in the wheel or bars. When I got home, I also flipped the bike upside down and the front wheel and handle bars seem fine.

Could this just be the wind and the panniers throwing me off a bit? I'm also not very heavy, so I wonder if that may make it more noticeable? I weigh about 120, with most of my weight in my lower body (aka not over the front of the bike), and I'm guess I had about 20-30lbs on my panniers, though not distributed 50/50. I'm just hoping that this wobble is normal and something I'll learn to counterbalance, and not something wrong with my bike!

Some pics of the setup will help others who run a rack and panniers to see if there is anything wrong there. I've found I just don't like the way racks and panniers handle, but that's because I like aggressive bikes. Something like a Fuji hybrid should do fine. Also, is this while you're sitting down and riding, or standing up and pedaling? Anything specific that you were doing on the bike that would trigger the feeling?

I'm attaching an image of the set up, though I'm not sure how much it'll clarify. I didn't notice any wobble when I was standing and pedaling. I only noticed it when I was sitting and after it got windy . . .

panniers.jpg

Having more weight on your bike does change how your bike handles. Not having been there, it's hard to know if anything's wrong, but I'd guess it's just not being used to the weight distribution. Moving 20-30 lbs from your back to your bike significantly changes the balance between dead weight (weight that just sits there and falls the way gravity wants it to) and live weight (weight that shifts around to keep the bike upright and holding a line).
It's not harder to ride straight with panniers, just different.
I typically ride with only one pannier, and the only time I've noticed the lack of balance was when I had 2000 sheets of paper on the one side.
Make sure that the pannier is firmly attached top and bottom, so the weight doesn't shift, and other than that, it's just a matter of riding. In a week, you won't even notice they're there.

more weight to the rear will make a bike that has a problem with speed wobble worse. I.e., it will wobble at a lower speed.

Not really normal for even heavy rear panniers to make the the front end of the bike wobbly.

Could be several things, but when looking at the picture, I suspect the big grocery bag pannier is the culprit: It is big and bulky and doesn't look stiff at all. I suspect that it will swing out of frequency when loaded, causing a slight but unpleasant feeling of bike shimmy. The rack looks like a two-legged alu-rack without side-rails. Those can be quite noodly and cause cause shimmy a low speeds, just like an unsecured rack (broken bolt etc) can cause shimmy.

Wind gusts probably makes the problem worse, and a loosely fitted attachment system like broad hooks and an elastic bungee can compound the problem too.

So check your rack, and try to fit the pannier so snugly and tight to the rack as possible. Try rocking the bike back and forth and from side to side and watch/feel how the panniers behave; do they work as inertia systems that wants to continue when the bike stops? Do they rattle a lot and move back and forth on the rack rails? Does the grocery pannier wobble like jelly when loaded? etc.

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Regards

Which Crosstown model? I had to check out Fuji's site (as they're rather rare around where I live/work) and at least one of the models has a suspension fork.

Did you have a lot of weight in the panniers?

I've never had a front wobble due to pannier weight, but if the rack starts flexing the bike feels weird. It feels really unstable. This was on my LHT - one of the most stable bikes known to man.

Also, you might try strapping the bag horizontally so it's not waving around with its load.

Lastly, if it's a front-back balance issue, you might dampen the oscillations by simply leaning forward when it starts, to put more weight on the front of the bike.